You can ask developers questions about Stylo in the #servo IRC channel (irc.mozilla.org/servo), if you find a bug please file it in our Bug tracker, Bugzilla. The component to file your bugs in is Core::CSS Parsing and Computation and start your summary field with Stylo:.

Stylo is making Firefox Nightly rendering of pages even faster and we are now working on chasing correctness and stability bugs so as to ship Stylo by default in Firefox 57, help us build this faster browser today, find and report bugs!

2017-09-06 update:

Stylo is now enabled by default on Nightly, wgich means that layout.css.servo.enabled is now set to True by default.

This article needs a tiny bit of JS so that it changes the title to “Stylo is ready for community testing by you, right now!” as a little reward for people who are reading this article while already using Nightly =)